In recent years, all operations of a camera significant to image capture, such as operation for determining the exposure and a focusing operation, may be performed automatically. Accordingly, even a user who is not accustomed to using a camera may nearly always succeed in taking high quality pictures.
In addition, recently marketed cameras include an image stabilization control apparatus, which includes a vibration correction unit, a driving unit, and a vibration detection unit and are configured to prevent image shake occurring due to vibration. By using such recent cameras, a photographer may nearly always succeed in taking high quality pictures.
An image stabilization control apparatus configured to prevent image shake is briefly described below. The hand shake that may occur with a camera during capture is a vibration with a frequency of, generally 1 to 10 Hz. To take a photograph without any image shake even when such vibration is applied to a camera when the shutter release button is pressed, it is necessary to detect the vibration applied to the camera and displace a lens for correcting image shake (hereinafter simply referred to as a “correction lens”) according to the detected value.
Therefore, in order to shoot an image without any image shake even when camera undergoes vibration, it is necessary to detect a precise level of the vibration on the camera and to correct the variation in the optical axis occurring due to the vibration. The vibration (on a camera) can be calculated, in principle, by using a vibration detection unit provided on the camera. More specifically, such a vibration detection unit detects the acceleration, the angular acceleration, the angular velocity, and the angular displacement and executes an operation on an output thereof to correct image shake.
Under general capture conditions, angular vibration (rotational vibration), which may occur according to the orientation of the camera, is the primary cause of the possible vibration. Therefore, a conventional camera includes an angular velocity meter only to detect vibration. In such a camera, it is intended that image shake be suppressed by driving a vibration correction unit (i.e., a correction lens), which displaces the optical axis according to a signal from the vibration detection unit, with a driving unit.
Meanwhile, when an image is taken at a close distance (under a capture condition in which a high imaging magnification is used), significant image degradation due to parallel vibration, which may otherwise cause little image degradation, may occur in addition to angular vibration, which may occur due to the orientation of the camera. Under capture conditions in which an object image is taken at such a close object distance as about 20 cm as in the case of macro photography, or if the focal length of an imaging optical system is very large (400 mm, for example) even when a sufficient object distance of 1 meter is secured, it becomes necessary to positively detect the parallel vibration and drive the vibration correction unit.
In this regard, in a method discussed in Japanese Patent Application Laid-Open No. 07-225405, an accelerometer configured to detect acceleration is provided to detect parallel vibration and drive a vibration correction unit according to the detected parallel vibration value and an output from an angular velocity meter, which is provided separately.
Furthermore, a method discussed in Japanese Patent Application Laid-Open No. 2002-359769 corrects image shake while changing the amount of correcting the vibration. In this method, an image sensor of a camera acquires motion information of a captured image while correcting the image shake. This method sets an optimum vibration correction amount by evaluating the accuracy of image shake correction according to output from the image sensor.
In this regard, however, in the method discussed in Japanese Patent Application Laid-Open No. 07-225405, output signal from the accelerometer, which is used in detecting parallel vibration, may vary due to disturbance noise or environmental variation such as temperature change. Accordingly, it is difficult to correct parallel vibration with high accuracy.
Furthermore, in the method discussed in Japanese Patent Application Laid-Open No. 2002-359769, setting an optimum vibration characteristic requires a large amount of time. Accordingly, the user operability of the camera may be degraded. In addition, mechanical parts of the vibration correction unit become large to achieve a variable vibration correction amount.